Cognitive impairment in MS: rehabilitation approaches.

Cognitive deficits have been reported in 45%-70% of patients with multiple sclerosis (MS). Like other symptoms of MS, cognitive deficits are highly variable. Slowed information processing and memory and learning dysfunction are regarded as the most frequent cognitive deficits in MS. Both white and gray matter damages have been suggested to contribute to cognitive impairments in MS. There is no direct relationship between cognitive deficits and physical disability, disease duration or course of the disease. In addition to cognitive impairments, neuropsychiatric symptoms are observed in MS, the most common being alterations in mood state. Neurobehavioral deficits have multidimensional effects on the activities of daily living and quality of life. Consequently, attention should be paid to early diagnosis and treatment. Based on studies on cognitive retraining and more multimodal neuropsychological rehabilitation, both approaches show promise in the treatment of cognitive impairments and their harmful effects. This review introduces the frequency and characteristics of cognitive impairments, as well as main findings on the effects of neuropsychological rehabilitation in MS.

Asymptomatic subjects differ less from their twin siblings with MS than from healthy controls in cognitive functioning. A Finnish Twin Cohort study.

BACKGROUND: Cognitive impairment develops in some MS patients at any time during the course of the disease regardless of whether the patients have neurological disability or not. Underlying causes for the MS related cognitive decline are yet poorly understood but both genetic and environmental risk factors have been proposed. OBJECTIVES: To assess whether the cognitive performance differs between subjects with multiple sclerosis (MS) and their asymptomatic co-twins. METHODS: Nineteen twin pairs discordant for MS recruited from the Finnish Twin Cohort were studied neurologically and with a comprehensive neuropsychological test battery. Control group included twenty age and education matched healthy subjects. RESULTS: Compared with the control subjects, the asymptomatic co-twins of MS patients performed significantly less well in tests of naming, verbal reasoning, visuospatial performance, processing speed, attention, verbal memory and learning. The twins with MS performed significantly less well than their co-twins in the SDMT evaluating processing speed, in visual learning and in word fluency. CONCLUSIONS: The lack of significant difference in majority of neuropsychological tests between the MS patients and their co-twins as well as considerable differences between asymptomatic co-twins and healthy controls may suggest that the cognitive performance may be partly developmental and regulated both by genes and shared environmental factors.

Relationship between subjective and objective cognitive performance in multiple sclerosis.

OBJECTIVES: Self- and informant reports of patients' cognitive performance are an important source of information for clinicians to consider in neuropsychological evaluation. The aim of the study was to find out whether the relationship between subjective or informant observations of cognitive deterioration and objective cognitive performance differ in patients with relapsing and progressive multiple sclerosis (MS). MATERIALS & METHODS: One ninety-six MS patients (relapsing-remitting n = 138; progressive n = 58) underwent neuropsychological assessment with the Brief Repeatable Battery of Neuropsychological Tests. Subjective and informant-reported cognitive symptoms, mood, impact of the disease, and quality of life were evaluated with self-reports. According to consistency of evaluations, patients and informants were classified as accurate estimators (consistent subjective and objective cognitive performance), underestimators (subjectively but not objectively cognitively impaired), or overestimators (objectively but not subjectively cognitively impaired). RESULTS: Patients' and informants' reports on patients' cognitive performance were approximately equally appropriate, slightly over half being accurate. Mood was associated with patients' subjective cognitive complaints. The relapsing group reported more subjective cognitive symptoms than the progressive group, although the objective cognitive performance did not differ between the groups. Overestimation occurred especially among patients with more severe physical disability, progressive phenotype of the disease, more pronounced cognitive impairment, and less education. CONCLUSIONS: Slightly over half of patient and informant observations of cognitive deterioration were appropriate. Patients with progressive phenotype were more prone to overestimation than patients with relapsing phenotype.

The progress of cognitive decline in newly diagnosed MS patients.

OBJECTIVES: Cognitive impairment occurs in multiple sclerosis already in the early stages of the disease. Less is known about the evolution of cognitive decline, especially in newly diagnosed MS patients. The results of existing studies are contradictory in that both cognitive preservation and progressive deterioration have been reported. The purpose of this study was to examine how cognitive impairment evolves over time in the early stages of MS. MATERIAL AND METHODS: At baseline, the participants were 36 newly diagnosed MS patients and 37 controls. A group of 30 patients were followed longitudinally at a mean test-retest interval of 6.1 years. The test battery covered attention, information processing, memory and learning, verbal and motor functions and reasoning. RESULTS: There was a significant decline in divided attention (dual task) and information-processing speed (SDMT) at follow-up, but no significant deterioration in overall cognitive performance. CONCLUSIONS: Overall cognitive functioning remained quite stable during the 6-year follow-up, whereas divided attention and processing speed deteriorated. However, deterioration in performance on the SDMT and the dual task does not seem to indicate more extensive cognitive deterioration. Given the impact of cognitive impairment on patients' quality of life, early detection of its occurrence in MS is extremely important.

The effects of heat stress on cognition in persons with multiple sclerosis.

BACKGROUND: Heat sensitivity and cognitive deficits are typical manifestations of multiple sclerosis (MS). Although cognitive deficits are quite well characterized, practically no data exist on the effects of heat on cognitive performances in MS. OBJECTIVE: To assess the effects of short-term heat stress on cognitive functioning in subjects with MS. METHODS: A total of 23 heat-sensitive MS and 19 healthy control (HC) subjects participated. Moderate heat exposure took place in a Finnish sauna. Cognitive functioning was measured with tests of sustained attention and processing speed, the Paced Auditory Serial Addition Test (PASAT 3" and 2") and the computerized visual vigilance test, before, during and after heat exposure. RESULTS: During the heat exposure, the core body temperature of the MS group rose significantly more (p = 0.002) than that of the HC group. The heat stress worsened the performance of the MS group in the PASAT 3" (p = 0.025) but not in the other cognitive measures. The performance in the PASAT 3" was reversed almost to the baseline level only 1- h after the heat exposure. CONCLUSIONS: A significant increase in core body temperature during heat stress is associated with a mild and reversible worsening of the PASAT 3" performance, while visual vigilance performance seems to remain almost unaffected.

Recommendations for a Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS).

BACKGROUND: Cognitive impairment in MS impacts negatively on many patients at all disease stages and in all subtypes. Full clinical cognitive assessment is expensive, requiring expert staff and special equipment. Test versions and normative data are not available for all languages and cultures. OBJECTIVE: To recommend a brief cognitive assessment for multiple sclerosis (MS) that is optimized for small centers, with one or few staff members, who may not have neuropsychological training and constructed to maximize international use. METHODS: An expert committee of twelve members representing the main cultural groups that have so far contributed considerable data about MS cognitive dysfunction was convened. Following exhaustive literature review, peer-reviewed articles were selected to cover a broad spectrum of cultures and scales that targeted cognitive domains vulnerable to MS. Each was rated by two committee members and candidates scales were rated on psychometric qualities (reliability, validity, and sensitivity), international application, ease of administration, feasibility in the specified context, and acceptability to patients. RESULTS: The committee recommended the Symbol Digit Modalities Test, if only 5 minutes was available, with the addition of the California Verbal Learning Test - Second Edition and the Brief Visuospatial Memory Test - Revised learning trials if a further 10 minutes could be allocated for testing. CONCLUSIONS: A brief cognitive assessment for MS has been recommended. A validation protocol has been prepared for language groups and validation studies have commenced.

The effects of rivastigmine on processing speed and brain activation in patients with multiple sclerosis and subjective cognitive fatigue.

BACKGROUND: Cognitive decline and fatigue are typical in multiple sclerosis (MS). However, there is no official medication for either of these symptoms. OBJECTIVE: The purpose of this study was to estimate the effects of a single dose of rivastigmine on processing speed and associated brain activity in patients with MS and subjective cognitive fatigue. METHODS: Fifteen patients with MS and subjective cognitive fatigue and 13 healthy controls (HCs) matched for age, gender and education performed a neuropsychological assessment and functional (f)MRI. A modified version of the Paced Visual Serial Addition Test (mPVSAT) was used as the behavioural task during fMRIs. After the first scanning session, both groups were randomly divided into two subgroups receiving either rivastigmine or placebo. A single dose of rivastigmine or placebo was administrated double-blindly and 2.5 hours later the scanning was repeated. RESULTS: At baseline, the patients with MS showed slower processing speed in mPVSAT compared with the HCs. They also demonstrated stronger bilateral frontal activation after sustained cognitive effort than the HCs. Performance improvement and a further activation increase in the left anterior frontal cortex and additional activation in the right cerebellum were observed in patients who received rivastigmine but not in patients on placebo, or in HCs with placebo or rivastigmine. CONCLUSION: These preliminary findings suggest that rivastigmine may improve cognitive processing speed by enhancing compensatory brain activation in patients with MS.

Cognitive dysfunction in primary progressive multiple sclerosis: a neuropsychological and MRI study.

Although cognitive dysfunction is known to occur in multiple sclerosis (MS), only few studies have reported cognitive performance in patients with primary progressive MS (PPMS). To find out the pattern of cognitive performance in PPMS, 28 PPMS patients underwent an extensive battery of neuropsychological tests. The results were compared to those of healthy controls (n = 20) and patients with secondary progressive MS (SPMS, n = 28). Furthermore, the results of neuropsychological tests in PPMS were correlated to magnetic resonance imaging findings. Our study showed that the PPMS patients have deficits in several cognitive domains when compared to age-matched and education-matched controls, but the cognitive impairment in the PPMS and SPMS patients appeared to be similar. Cognitive deficits in PPMS patients correlated with diffuse brain lesion, T1- and T2-lesion load, but no correlations were found with atrophy.

Social competence of preschool children with epilepsy.

The aims of this study were to describe the social competence of 3- to 6-year-old children with epilepsy (n=26) compared with that of age- and gender-matched healthy controls (n=26). Social competence was assessed with the Vineland Social Maturity Scale, Conners' Parent Rating Scales-Revised, and the Child Behavior Checklist. The results indicate that the children with epilepsy, especially with complicated epilepsy, had fewer age-appropriate social skills and more attention and behavior problems than the healthy children, as reported by parents. It is possible that the lack of age-appropriate social skills and the presence of attention problems predispose to behavioral problems. Also, epilepsy-related factors impaired the achievement of social competence. This study shows that the preschool children with complicated, early-onset epilepsy are at increased risk of difficulties in social competence.

The reliability of the MSFC and its components.

BACKGROUND: The Multiple Sclerosis Functional Composite (MSFC) is a multidimensional measurement tool for multiple sclerosis (MS) including a measure of ambulation (Timed 25-foot Walk [TWT]), arm function (Nine-Hole Peg Test [9HPT]) and cognition (Paced Auditory Serial Addition Test [PASAT]). OBJECTIVES: To assess the reliability and practice effects in the Finnish version of the MSFC and its components. MATERIALS AND METHODS: Ten relapsing-remitting MS patients and 10 healthy controls underwent five testing sessions with the MSFC over a 4-week period. RESULTS: The MSFC showed excellent intra- (0.99) and inter-rater (1.0) reliability. The MSFC, especially the 9HPT and the PASAT showed significant practice effects. On the 9HPT the controls remained stable whereas the patients improved their performance; on the PASAT both groups improved. CONCLUSIONS: The MSFC showed excellent intra- and inter-rater reliability although the 9HPT and the PASAT were prone to considerable practice effects.

The PASAT performance among patients with multiple sclerosis: analyses of responding patterns using different scoring methods.

The Paced Auditory Serial Addition Test (PASAT) is widely used in the evaluation of multiple sclerosis (MS) patients' cognitive performance, and also used as the sole measure of cognition in a recently developed assessment tool for MS clinical trials, the Multiple Sclerosis Functional Composite (MSFC). We analysed if MS patients and healthy controls have different patterns of responding in the PASAT, and whether different scoring methods influence the PASAT's sensitivity and specificity in detecting disease-associated cognitive impairment. Forty-five relapsing-remitting MS patients and 48 healthy controls were evaluated using the PASAT and a comprehensive neuropsychological examination. Cognitively deteriorated MS patients compensated for their difficulties in PASAT by omitting rather than guessing answers. They skipped items intermittently, which reduces the difficulty of the task. Furthermore, towards the end of the PASAT's 60-item series MS patients' performance had a trend to fade whereas controls' performance was more even throughout the task. The dyad score or the percent dyad score did not essentially improve the sensitivity or the specificity, but the accuracy improved when the answers at the end of the PASAT series were specifically emphasized. Using the combined score, 73% of the patients were correctly classified as cognitively impaired or unimpaired.

Patient information on cognitive symptoms in multiple sclerosis - acceptability in relation to disease duration.

OBJECTIVE: Recently, regular cognitive screening assessments have been advised in multiple sclerosis (MS). No studies have been carried out yet on the acceptability of information on cognitive deficits among MS patients. MATERIALS AND METHODS: Translation of an information booklet developed by a working group of European MS Rehabilitation Centers. Distribution of the booklet among 133 MS patients of two rehabilitation units and one outpatient clinic together with a one-page questionnaire. RESULTS: The booklet was highly understandable and rated to give moderate new information. Overall, the brochure was perceived as encouraging but significantly less so (P = 0.014) in recently diagnosed patients. Patients with subjectively perceived deficits considered the brochure to be significantly more relevant (P = 0.002). CONCLUSION: Information on cognitive deficits does not increase fears even in recently diagnosed MS patients. Patients with perceived deficits found the information more relevant than others and also less familiar. Thus, it seems appropriate to offer information about cognitive impairments to MS patients.

Changes in physical performance among high-functioning older adults: a 6-year follow-up study.

Purposes of the study were (1) to investigate changes in physical performance during 6 years follow-up among high-functioning older adults and (2) to describe the selection of study sample with reference to measured performance. Subjects (n=1,133) born during 1917-1941 participated in the battery of health-related fitness (HRF) tests (6.1-m walk, stair climbing, backwards walk, trunk side-bending, dynamic back extension, 1-km walk and body mass index) in 1996. Six hundred and six subjects were retested in 2002. In general, poorer fitness in the baseline assessment predicted non-participation in retesting as well as test exclusions and interruptions in retesting. The 6-year changes in the HRF showed a linear trend (P<0.01) according to age group: performance of older groups deteriorated on average more than the performance of younger groups. In most of the tests, gender was statistically significantly (P<0.05) associated with the changes in performance. The mean performance of the women deteriorated in all tests during the follow-up, while the mean performance of the men deteriorated only in the trunk side-bending, 6.1-m walk and 1-km walk tests. It can be concluded that among the subjects who participated in the follow-up testing, older age and being a woman increased deterioration in several components of HRF. Considering the selection of the subjects, the deteriorations identified are very likely underestimations of real fitness changes among this sample.

Sleep apnoea: Finnish National guidelines for prevention and treatment 2002-2012.

(1) After negotiations with the Finnish Ministry of Social Affairs and Health, a national programme to promote prevention, treatment and rehabilitation of sleep apnoea for the years 2002-2012 has been prepared by the Finnish Lung Health Association on the basis of extensive collaboration. The programme needs to be revised as necessary, because of the rapid development in medical knowledge, and in appliance therapy in particular. (2) Sleep apnoea deteriorates slowly. Its typical features are snoring, interruptions of breathing during sleep and daytime tiredness. Sleep apnoea affects roughly 3% of middle-aged men and 2% of women. In Finland, there are approx. 150,000 sleep apnea patients, of which 15,000 patients have a severe disease, 50,000 patients are moderate and 85,000 have a mild form of the disease. Children are also affected by sleep apnea. A typical sleep apnea patient is a middle-aged man or a postmenopausal woman. (3) The obstruction of upper airways is essential in the occurrence of sleep apnoea. The obstruction can be caused by structural and/or functional factors. As for structural factors, there are various methods of intervention, such as to secure children's nasal respiration, to remove redundant soft tissue, as well as to correct malocclusions. It is possible to have an effect on the functional factors by treating well diseases predisposing to sleep apnoea, by reducing smoking, the consumption of alcohol and the use of medicines impairing the central nervous system. The most important single risk factor for sleep apnoea is obesity. (4) Untreated sleep apnoea leads to an increase morbidity and mortality through heart circulatory diseases and through accidents by tiredness. Untreated or undertreated sleep apnoea deteriorates a person's quality of life and working capacity. (5) The goals of the Programme for the prevention and treatment of sleep apnoea are as follows: (1) to decrease the incidence of sleep apnoea, (2) to ensure that as many patients as possible with sleep apnoea recover, (3) to maintain capacity for work and functional capacity of patients with sleep apnoea, (4) to reduce the percentage of patients with severe sleep apnoea, (5) to decrease the number of sleep apnoea patients requiring hospitalisation and (6) to improve cost effectiveness of prevention and treatment of sleep apnoea. (6) The following means are suggested for achieving the goals: (1) to promote prevention of obesity, weight loss and weight control; (2) to promote securing of nasal respiration in child patients and removal of obstructing redundant soft tissues; (3) to promote the correction of children's malocclusions, (4) to enhance knowledge about risk factors and treatment of sleep apnoea in key groups, (5) to promote early diagnosis and active treatment, (6) to commence rehabilitation early and individually as a part of treatment and (7) to encourage scientific research. (7) On the national level, the occurrence of sleep apnoea can be prevented, for example, by encouraging weight control. The programme gives examples of such measures and appeals to various authorities and voluntary organisations to reinforce their collaboration. Preventive measures should be individualised, and based on due consideration. (8) The efficacy of diagnosing sleep apnoea should be increased. Attention should be paid to the symptoms of risk group patients at different units of the primary and occupational health care. Even mild forms of the disease should be treated appropriately. Diagnosis and treatment of the disease involve cooperation between the primary and specialised health-care sectors. Methods of treatment are (1) treatment of obesity, (2) positional therapy, (3) reduction of the use of medicines impairing the central nervous system, (4) reduction of smoking and the consumption of alcohol, (5) devices affecting the position of the tongue and lower jaw, (6) treatment with Continuous Positive Airway Pressure (CPAP-treatment), (7) surgical methods of treatment and (8) rehabilitation. (9) The hierarchy of referrals in the prevention and treatment of sleep apnoea should be revised to accord a greater role to the primary health-care sector. Good exchanges of information and cooperation between the primary health care and specialised medical-care sectors should be developed. Hospitals districts in cooperation with provincial governments and municipalities should ensure that different levels of the health-care system are capable of fulfilling the tasks assigned to them appropriately. (10) Rehabilitation of sleep apnoea should be goal-orientated and cover all forms of rehabilitation: medical, occupational and social. Rehabilitation should prevent the effects caused by the disease. Thus, it is possible to support self-care, increase the patient's resources and improve quality of life. (11) Information and training should be directed primarily towards health-care personnel, patients and their families. Organisations should produce materials for health and patient education as well as organising training events. To support the activities. financing will be needed from organisations such as Finland's Slot Machine Association. The Social Insurance Institution should disseminate information about questions of social security. Regional direction and training will mainly be the responsibilities of hospital districts, provincial governments and local health centres. The media will play an important role in the dissemination in-depth information about prevention and treatment of sleep apnoea.

Short-term effects of radiotherapy on attention and memory performances in patients with brain tumors.

BACKGROUND: The objective of the current study was to evaluate the short-term effects of radiotherapy on attention and memory performance in patients with brain tumors. METHODS: Thirteen patients underwent a neuropsychologic examination on three occasions: at baseline before radiotherapy, which lasted for 6 weeks; within 2 weeks after the completion of radiotherapy; and 3 months after the completion of radiotherapy. Thirty healthy individuals were studied at baseline as a control group. Verbal, visuomotor, and memory tests were administered. Attentional performances were examined using CogniSpeed reaction time software. RESULTS: At baseline, the patients scored significantly lower than the controls in tests of semantic memory (Similarities; P = 0.002), visuoconstructive skill (Block Design; P = 0.028), and visual and verbal memory (recall of 20 objects: immediate, P = 0.017; delayed, P = 0.002; recall of 30 paired word associates: immediate, P = 0.002; delayed, P = 0.005). The patients performed significantly more poorly than the control group on the Two-Choice Reaction Time test (P = 0.047), the Subtraction test (P = 0.042), and the Vigilance test (P = 0.023). After radiotherapy, the performance of the patients did not worsen on any measure, whereas their conscious cognitive processing was improved (P = 0.002). CONCLUSIONS: Treatment with radiotherapy did not cause negative short-term effects on attentional and memory functions in patients with brain tumors who received a radiation dose of 54.5 grays. The cognitive deficits found in these patients were evident at baseline before radiotherapy. Thus, it seems likely that the deficits were associated with the tumor itself and/or the surgical procedures.

Visual object recognition in multiple sclerosis.

Deficits in tasks measuring visual processing have been earlier reported in studies of MS. Yet, the nature and severity of visual-processing deficits in MS remains unclear. We used a new method in order to measure the different stages of visual processing in object recognition: shape recognition, familiarity recognition, semantic categorization, and identification with naming. Six two-choice reaction-time tasks were presented to 30 MS patients and 15 healthy controls. The patients were divided into cognitively preserved and cognitively deteriorated study groups according to their cognitive status. The purpose was to find out whether deficits at specific stages of visual processing can be found in cognitively deteriorated MS patients. Cognitively deteriorated MS patients did not perform as well as cognitively preserved MS patients or healthy controls. They were slower already at the early stage of visual processing where discrimination of whole objects from scrambled ones was required. They also had higher error rates in tasks requiring object familiarity detection and object identification with naming. Thus, cognitively deteriorated MS patients had difficulties in visual shape recognition and semantic-lexical processing. However, variation of performances was large within both of the patient groups indicating that even patients without a generalized cognitive decline may have deficits in some stages of the visual processing. We suggest that because of the heterogeneity of the patients, every single case needs to be examined separately in order to identify the possible deficits in visual processing.

Sematic memory deficit in multiple sclerosis; impaired understanding of conceptual meanings.

The aim of the present study was to determine whether a cognitive decline, related to multiple sclerosis (MS), also involves deficits in semantic memory. Semantic memory function was evaluated by studying the conscious understanding of conceptual meanings. A group of MS patients with cognitive decline was presented with four tasks concerning concepts, their attributes and relationships to other concepts. The tasks were designed to measure spontaneous, cued and recognition performance separately. The patients had difficulties in understanding conceptual meanings. Easing the retrieval demands of the tasks did not help them to improve their performance which was poorer than the control group's on every task used. The results indicate a retrieval deficit combined with an underlying storage deficit in the semantic memory of MS patients with cognitive decline.

Relationship of metabolic variables to abdominal adiposity measured by different anthropometric measurements and dual-energy X-ray absorptiometry in obese middle-aged women.

OBJECTIVES: To investigate how abdominal adiposity assessed by different anthropometric measurements and dual-energy X-ray absorptiometry measurements is associated with metabolic risk factors for cardiovascular disease and non-insulin-dependent diabetes mellitus in obese women. DESIGN: Cross-sectional study. SUBJECTS: Forty-three healthy, obese, middle-aged women (age: 29-64 y, BMI: 28-42 kg/m2). MEASUREMENTS: (1) Anthropometry: waist circumference, waist-to-hip ratio, waist-to-height ratio, abdominal sagittal and transverse diameters and their ratio. (2) Dual-energy X-ray absorptiometry: the amount of total and regional abdominal fat. (3) Metabolic measurements: serum total, VLDL, LDL, HDL cholesterol, triglycerides, fasting and postglucose serum insulin and glucose. RESULTS: After adjustment for age and BMI, all the anthropometric measurements except waist-to-hip ratio and waist-to-height ratio related significantly to HDL and LDL cholesterol. On the other hand, waist-to-hip ratio and waist-to-height ratio showed an association with triglycerides. In addition, all the anthropometric measurements except transverse diameter correlated significantly with fasting insulin and fasting glucose. Waist-to-hip ratio was the only measure that associated with 2 h glucose concentration. The differences between the correlation coefficients were not statistically significant in the z-transformed correlation coefficient test. As to dual-energy X-ray absorptiometry results, the region from the dome of diaphragm to the top of femur ('abdominal fat') and the area between the first and the fourth lumbal vertebrae ('upper lumbal fat') inversely related to HDL cholesterol and positively to triglycerides. Both of these regions correlated significantly with fasting insulin, and "upper lumbal fat' associated also with fasting glucose even after adjustment for age and BMI. CONCLUSION: None of the anthropometric measurements (waist circumference, waist-to-hip ratio, waist-to-height ratio or sagittal diameter) was significantly superior to others to assess the metabolic risk profile. 'Upper lumbal fat' (the area between the first and the fourth lumbal vertebrae) measured by dual-energy X-ray absorptiometry discerned obese women with elevated fasting insulin and fasting glucose.

Effect of photorefractive keratectomy on the accuracy of pneumatonometer readings in rabbits.

PURPOSE: To determine whether measurement of intraocular pressure (IOP) using a pneumatonometer is reliable after myopic 5 or 15 D excimer laser photoablation in rabbits. METHODS: Ten rabbits underwent 5 D myopic photorefractive keratectomy (PRK) of the left eye. Another seven rabbits underwent 15 D PRK: The right eye served as a control. The diameter of each PRK was 5 mm. Rabbits were examined 2.5 to 3 months later under general anesthesia. Eyes were cannulated, and the IOP was maintained at 5 to 40 mm Hg and measured using an intracameral manometer and a pneumatonometer at each pressure level; approximately 50 pressure points were formed. Readings of the two techniques were compared. RESULTS: Linear regression analysis comparing manometric and pneumatonometric readings revealed the following data in eyes with 5 D corrections (n = 10): correlation coefficient (r) = 0.926, slope = 1.058, and intercept = -3.133. The values of the unoperated control eyes were: r = 0.900, slope = 0.962, and intercept = -1.010. The following results were obtained in eyes with 15 D photoablation (n = 7): r = 0.876, slope 1.133, and intercept -3.147. Values for the control eye were: r = 0.885, slope = 1.175, and intercept = -3.497. When the manometer and pneumatonometer readings of all animals were compared, the adjusted squared correlation coefficient was 79%. When the variabilities associated with the animals and the PRK procedure (pooled 5 and 15 D corrections) were taken into account, adjusted squared correlation coefficient increased from 8% to 87%. CONCLUSIONS: Photorefractive keratectomy as high as 15 D/5 mm had only a minor effect on pneumatonometer readings in rabbits, indicating that the elastic properties of the cornea related to the accuracy of pneumatonometry were not significantly altered. Postoperative IOP monitoring with tonometers, based on flattening of the cornea under pressure, is accurate after PRK.